Continuous processes of chemical nickel plating



United States CONTINUOUS PROCESSES OF CHEMICAL NICKEL PLATING No Drawing. Application April 6, 1956 Serial No. 576,533

7 Claims. (Cl. 117-430) The present invention relates to continuous processes of chemical nickel plating, and more particularly to improved processes of the general character of that disclosed in the copending application of Gregoire Gutzeit, Paul Talmey and Warren G. Lee, Ser. No. 569,815, filed March 6, 1956.

It is a general object of the invention to provide a continuous process of chemically plating catalytic articles with nickel, employing an aqueous bath of the nickel cation-hypophosphite anion type, also containing lactic ions and propionic ions, and involving an improved regeneration procedure, wherein nickel ions and hypophosphite ions are progressively added to prevent the depletions thereof in the bath as the plating process proceeds, and lactic ions and propionic ions are progressively added to increase the concentrations thereof in the bath as the plating process proceeds.

Another object of the invention is to provide in a continuous chemical nickel plating process of the character mentioned, an improved method of regenerating the bath as the plating process proceeds and involving e tio the additions of nickel ions and hypophosphite ions to prevent the depletions thereof in the bath and involving the additions of lactic ions and propionic ions to increase the concentrations thereof in the bath, wherein the additions of lactic ions and propionic ions are related to the addition of nickel ions so that about 0.03 mole of lactic ions and 0.005 mole of propionic ions are added to the bath to each 0.08 mole of nickel ions added thereto.

A further object of the invention is to provide in the continuous process of chemical nickel plating, an improved method of regenerating the-bath of the character described, wherein the lactic ion addition and the propionic ion addition are .so controlled that the plating rate of the bath and the phosphite anion tolerance thereof are governed to obtain nickel plating under substantially ideal conditions.

Further features of the invention pertain to the'particular arrangement of the steps of the method, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the foregoing and following specification;

In the previously mentioned application of Gregoire Gutzeit, Paul Talmey and Warren G. Lee, there is disclosed a continuous chemical nickel plating process employing a continuous plating system of the character of that disclosed in U. S. Patent No. 2,717,218, granted on September 6, 1955, to Paul Talmey and William J. Crehan, and involving an aqueous bath of the nickel cation-hypophosphite anion type, also containing lactic ions and propionic ions.

Specifically, in the continuous plating system of Paul Talmey and William J. Crehan, the plating solution is circulated from a reservoir through a condenser to a asserts Patented June 3,

plating chamber and thence through a flash tank back to the reservoir. In the reservoir, the plating solution is held at a storage temperature well below the boiling point thereof (such, for example, as a temperature of about l50 F.); in the plating chamber, the plating solutionis held at a plating temperature near the. boiling point thereof (such, for example, as a temperature of about 210? R); in the condenser, live steam is injected into the plating solution to eifect the requiredheating thereof; and in the flash tank, water vapor is withdrawn from the plating solution to effect the required cooling thereof. Also in the system, a balance is maintained between the live steam injected into the plating solution in the condenser and the Water Vapor withdrawn from the plating solution in the flash tank so as to prevent overall expansion or contraction of thevolume of the plating solution. Of course, catalytic articles are plated with nickel in the plating chamber by immersion in the hot plating solution; such catalytic articles being initially pretreated to prepare the surfaces thereof in a conventional manner; and such catalytic articles normally comprise a catalytic surface formed of iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, aluminum, copper, silver and gold, as is well-understood.'

As disclosed in the Gutzeit; Talmey and Lee application, the plating bath essentially comprises an aqueous solution comprising nickel ions, hypophosphite ions, lactic ions and propionic ions. In the bath: the nickel ions may be derived from nickel chloride, nickel sulfate, nickel hypophosphite, etc.; the 'hypophosphite ions may be derived from sodium hypopho sphite, nickelhypophosacid or appropriate soluble propionates. For example,

typical plating baths of this character may essentially comprise:

Nickel ions (as nickel sulfate).. m. p. l 0.07-0.08 Hypophosphite ions (as sodium hypophosphite) m. p. 1;. 0225-0230 Lactic ions (as lactic acid) m. p.l 0.25-0.60 P'ro'pionic ions (as propionic acid) on. p. l-.. 0.025-.0.060

'l hese plating baths are very advantageous in the platingofcatalytic articles by virtue of the fact that they havea high plating rate of at least 1 mil/hour, or' ex pressed inc. g. s. units, of at least 3.5 l0 gm./cm. min., and have a high phosphite tolerance inhibiting the precipitation of nickel phosphite even at a phosphite ion concentration in some cases very close to 1.0 m. p. 1. Further, the plating appearance on both metals and properly prepared non-metals is excellent (bright, smooth and non-porous) and adhesion of the nickel plating on both metallic and non-metallic bodies is excellent (no flaking of the nickel coating in bending, abrading and shock tests) In these plating baths, the lactic ion serves both as an exalting additive (increasing the normal plating rate thereof) and as a complexing or chelating agent (tying-up the nickel ions to prevent the precipitation of nickel phosphite or basic nickel 'salts); while the propionic ions serve fundamentally as a supplemental exalting additive. In

these plating baths, the phosphite tolerance is substam tially directly porportional to the lactic ion concentration, whereas the plating rate is maximized within an optimum range of lactic ion concentration of about 0.15 to 0.45 m. p. 'l., the optimum range of propionic ion concentration being about 0.015 to0.045 m. p. l.

.The characteristics of these plating baths were established by a series of plating tests that were conducted in 10-minute rate tests utilizing steel samples (Dayton- Rodgers) of 20 cm. total area that had been properly prepared by vapor degreasing, cleaned by an alkaline soak and lightly pickled in 1:1 hydrochloric acid. The steel samples thus prepared were then plated at 98:1" C. in 50 cc. of diiferent plating baths each containing nickel cations (as nickel sulfate) 0.08 m. p. l., hypophosphite ions (as sodium hypophosphite) 0.224 m. p. 1., and the indicated amounts of organic additives, the pH being adjusted with NaOH to about 4.7.

The results of these plating tests are set forth in the table below:

TABLE I l Lactic anion coneentration, m. p. l 0. 08 0. l6 0. 24 0. 30 0. 40 0.60 Weight gain, gm.... 0. 0563 0. 0759 0. 0791 0. 0706 0. 0792 0. 0602 Plating rate, RXIO gm./cm. /Inin. 2. 82 3. S 3. 96 3. 53 3. 46 3.01 Initial pH 4. 67 4. 69 4. 68 4. 73 4. 08 4. 65 Final pH 3. 32 3. 63 3. S7 4. 02 4. l7 4. 37 Phosphite tolerance,

m. p. l 0. 18 0.35 0. 55 1 4 B891 pp 0) 0) 0) Plating pp 1 Clear Smooth and bright.

When a plating bath of the character disclosed in the Gutzeit, Talmey and Lee application is employed in a continuous chemical nickel plating system of the character disclosedin the Talmey and Crehan patent, there is a gradual build-up of phosphite anions therein as the hypophosphite anions are oxidized to phosphite anions incident to the reduction of the nickel cations to metallic nickel; and in order to prevent the depletion of nickel cations and hypophosphite anions, the plating bath is regenerated in the reservoir by the addition of nickel cations and hypophosphite anions thereto. Also hydroxyl anions are added to the bath so as to prevent substantial departure of the initial pH thereof, since hydrogen cations are produced incident to the reactions mentioned. Since the lactic anions and the propionic anions are not depleted in the reactions mentioned, it is not normally necessary to add additional such lactic anions and propionic anions incident to the regeneration of the bath as time proceeds. Also, it is noted that the regeneration of the plating bath is progressive and may be accomplished either continuously or periodically, continuous regeneration being preferred as a matter of simplicity; and, of course, in the regeneration aqueous stock solutions of the required ions are employed.

By regeneration of the plating bath in the manner described, the nickel turnover is normally about 400% before it is necessary to discard the plating bath as a consequence of the build-up therein of an undesirable high concentration of phosphite anions of the order of about 1 molar. For example, if the bath initially contains 0.08 m. p. l. of nickel ions, there has been a 400% turnover of nickel ions in the plating process when, in the regeneration, the total quantity of nickel ions added thereto is 0.32 m. p. l. Incident to each turnover of nickel ions, there is normally an increase in phosphite ions of about 0.24 m. p. l.; whereby the phosphite ion concentration in the plating bath reaches about 0.96 m. p. l. at the end of 400% turnover of nickel ions. Also, in the regeneration of the bath, it is normally necessary to add about 0.24 mole/liter of hypophosphite ion to each 0.08 mole/liter or" nickel ion, since the ratio between nickel cation utilization and hypophosphite anion utilization in the plating process is normally about 1:3.

In accordance with the present invention, the plating bath is composed comprising an absolute concentration of hypophosphite ions in the range 0.15 to 0.30 mole/liter, suflicient nickel cations to provide a ratio between the nickel cations and the hypophosphite ions in the range 0.25 to 0.60, an absolute concentration of lactic anions iii of about 0.30 mole/liter and an absolute concentration of propionic anions of about 0.03 mole/liter; and by way of illustration, the following bath is recommended:

Nickel ions (as nickel sulfate) m. p. 1-- 0.08 Hypophosphite ion (as sodium hypophosphite) m. p. l 0.24 Lactic ions (as lactic acid) m. p. l 0.30 Propionic ions (as propionic acid) m. p. l 0.03 pH 4.5-4.8

In this plating bath, the lactic ion concentration (in combination with propionic ion concentration) is selected to give a high plating rate of the order of 0.9-4.0 mil/hour with only a modest phosphite tolerance of the order of 0.20 mole/liter; whereby this plating bath, as composed, is satisfactory only in the initial portion of the continuous plating operation. However, since the plating bath contains practically no phosphite anions at this time, it is substantially ideally suited to the initial portion of the continuous plating operation. This plating bath is employed in the continuous plating system disclosed in the T almey and Crehan patent and is progressively regenerated in the reservoir as the plating process proceeds by the additions thereto of nickel cations, hypophosphite anions, lactic anions and propionic anions, as well as hydroxyl anions. Preferably the regeneration of the plating bath is accomplished on a continuous basis in the reservoir remote from the plating chamber from appropriate aqueous stock solutions containing the ions noted. Specifically sufiicient hydroxyl anions are continuously added to the plating bath in order to retain the initial pH of the plating bath at the selected 'value within the range 4.5-4.8, and the additions of nickel cations and hypophosphite anions may be made based upon the addition of hydroxyl anions. In any case, the additions of nickel cations and hypophosphite anions are such as substantially to maintain the concentrations of 0.08 m. p. l. and 0.24 m. p. 1., respectively, as previously noted.

On the other'hand, the additions of lactic anions and propionic anions were made entirely upon a basis related to the addition of nickel cations and upon the basis of about 0.03 mole of lactic anions and about 0.005 mole of propionic anions to each 0.08 mole of nickel cations. Accordingly, upon each turnover of nickel cations in the plating bath, as the plating process proceeds, the lactic ion concentration is progressively increased due to the accumulation, by about 0.03 mole/liter, and the propionic ion concentration is progressively increased, due to the accumulation, by about 0.005 mole/liter. This arrangement is very advantageous as it brings about a progressive increase of the phosphite anion tolerance only as the phosphite anion concentration therein progressively increases; whereby the plating rate of the plating bath is substantially maximized throughout the plating operation involving the several turnovers of nickel cations in the regeneration.

'The principal relationship mentioned will be readily understood from the following table:

TABLE u Progressive composition of the plating bath with to certain ions respect While the plating baths are normally discarded after use in the plating process, such that the nickel cation turnover reaches about 400%, this is not critical, and

the present regeneration procedure has been successfullycarried out such that the niskel cation turnover in the plating baths reached 750%.

In view of the foregoing, it will be understood that in accordance with the present method of regenerating the plaitng bath, the lactic anion concentration (together with the propionic anion concentration) is progressively increased from the initial concentration in the plating bath only as required progressively to increase the phosphite anion tolerance of the plating bath, as the concentration of phosphite anions is progressively increased therein as the plating process proceeds, whereby the lactic anion concentration (together with the propionic anion concentration) are maintained, as far as is permissible, within the range of maximum plating rates of the plating bath, thereby to insure high efiiciency of the continuous plating process with respect to utilization of materials, labor costs, etc.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In the continuous process of chemically plating with nickel articles essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum; wherein said articles are contacted with a bath comprising an aqueous solution of nickel ions and hypophosphite ions and lactic ions and propionic ions; and wherein said bath initially comprises an absolute concentration of hypophosphite ions in the range 0.15 to 0.30 mole/liter, suflicient nickel ions to provide a ratio between the nickel ions and the hypophosphite ions in the range 0.25 to 0.60, an absolute concentration of lactic ions of about 0.30 mole/liter, and an absolute concentration of propionic ions of about 0.03 mole/liter, and said bath has an initial pH in the range 4.5 to 4.8; the method of regenerating said bath as the continuous plating process proceeds comprising progressively adding thereto nickel ions and hypophosphite ions and lactic ions and propionic ions, whereby said progressive additions of nickel ions and hypophosphite ions are such as to prevent the depletions thereof in said bath as the continuous plating process proceeds and said progressive additions of lactic ions and propionic ions are such as to increase the concentrations thereof in said bath as the continuous plating process proceeds, wherein said additions of lactic ions and propionic ions are related to said addition of nickel ions so that about 0.03 mole of lactic ions and about 0.005 mole of propionic ions are added to said bath to each 0.08 mole of nickel ions added thereto.

2. In the continuous process of chemically plating with nickel articles essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum; wherein said articles are contacted with a bath comprising an aqueous solution of nickel ions and hypophosphite ions and lactic ions and propionic ions; and wherein said bath initially comprises an absolute concentration of hypophosphite ions in the range 0.15 to 0.030 mole/ liter, sufficient nickel ions to provide a ratio between the nickel ions and the hypophosphite ions in the range 0.25 to 0.60, an absolute concentration of lactic ions of about 0.30 mole/liter, and an absolute concentration of propionic ions of about 0.03 mole/liter, and said bath has an initial pH in the range 4.5 to 4.8; the method of regenerating said bath as the continuous plating process proceeds comprising continuously adding thereto nickel ions and hypophosphite ions and lactic ions and propionic ions, whereby said continuous additions of nickel ions and hypophosphite ions are such as to prevent the depletions thereof in said bath as the continuous plating process proceeds and said continuous additions of lactic ions and propionic ions are such as to increase the concentrations thereof in said bath as the continuous plating process proceeds, wherein said additions of lactic ions and propionic ions are related to'said addition of nickel ions so that about 0.03 mole of lactic ions and about 0.005 mole of propionic ions are added to said bath to each 0.08 mole of nickel ions added thereto.

3. In the continuous process of chemically plating with nickel articles essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum; Wherein said articles are contacted with a bath comprising an aqueous solution of nickel ions and hypophosphite ions and lactic ions and propionic ions; and wherein said bath initially comprises an absolute concentration of hypophosphite ions in the range 0.15 to 0.30 mole/liter, sufiicient nickel ions to provide a ratio between the nickel ions and the hypophosphite ions in the range 0.25 to 0.60, an absolute concentration of lactic ions of about 0.30 mole/liter, and an absolute concentration of propionic ions of about 0.03 mole/liter, and said bath has an initial pH in the range 4.5 to 4.8; the method of regenerating said bath as the continuous plating process proceeds comprising progressively adding thereto nickel ions and hypophosphite ions and lactic ions and propionic ions, whereby said progressive additions of nickel ions and hypophosphite ions are such as to prevent the depletions thereof in said bath as the continuous plating process proceeds and said progressive additions of lactic ions and propionic ions are such as to increase the concentrations thereof in said bath as the continuous plating process proceeds, wherein said additions of hypophosphite ions and lactic ions and propionic ions are related to said addition of nickel ions so that about 0.24 mole of hypophosphite ions and about 0.03 mole of lactic ions and about 0.005 mole of propionic ions are added to said bath to each 0.08 mole of nickel ions added thereto.

4. In the continuous process of chemically plating with nickel articles essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum; wherein said articles are contacted with a bath comprising an aqueous solution of nickel ions and hypophosphite ions and lactic ions and propionic ions; and wherein said bath initially comprises an absolute concentration of hypophosphite ions in the range 0.15 to 0.30 mole/liter, suffi cient nickel ions to provide a ratio between the nickel ions and the hypophosphite ions in the range 0.25 to 0.60, an absolute concentration of lactic ions of about 0.30 mole/liter, and an absolute concentration of propionic ions of about 0.03 mole/liter, and said bath has an initial pH in the range 4.5 to 4.8; the method of regenerating said bath as the continuous plating process proceeds comprising progressively adding thereto hydroxyl ions and nickel ions and hypophosphite ions and lactic ions and propionic ions, whereby said progressive addition of hydroXyl ions is such as to prevent substantial departure of said bath from said initial pH range as the continuous plating process proceeds and said progressive additions of nickel ions and hypophosphite ions are such as to prevent the depletions thereof in said bath as the continuous plating process proceeds and said progressive additions of lactic ions and propionic ions are such as to increase the concentrations thereof in said bath as the continuous plating process proceeds, wherein said additions of lactic ions and propionic ions are related to said addition of nickel ions so that about 0.03 mole of lactic ions and about 0.005 mole of propionic ions are added to said bath to each 0.08 mole of nickel ions added thereto.

5. The continuous process of chemically plating with nickel articles essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises providing a bath initially comprising an aqueous solution of about 0.08 mole per liter of nickel ion and about 0.24 mole per liter of hypophosphite ions and about 0.30 mole per liter of lactic ions and about 0.030 mole per liter of propionic ions and having an initial pH in the range 4.5 to 4.8, contacting said articles with said bath as required to produce desired nickel coatings thereupon, and regenerating said bath as the continuous plating process proceeds by progressively adding thereto nickel ions and hypophosphite ions and lactic ions and propionic ions, whereby said progressive additions of nickel ions and hypophosphite ions are such as to maintain substantially said initial concentration thereof in said bath as the continuous plating process proceeds and said progressive additions of lactic ions and propionic ions are such as to increase substantially said initial concentrations thereof in said bath as the continuous plating process proceeds, wherein said additions of lactic ions and propionic ions are related to said addition of nickel ions so that about 0.03 mole of lactic ions and about 0.005 mole of propionic ions are added to said bath to each 008 mole of nickel ions added thereto.

6. The continuous process set forth in claim 5, wherein said bath is used sufficiently long therein that the total of the additions of nickel ions thereto is at least about 400% of said initial concentration thereof in said bath.

7. The continuous process set forth in claim 5, wherein said oath is used sufiiciently long therein that the total of the additions of lactic ions thereto effects an ultimate concentration of lactic ions therein at least as great as about 0.40 mole/liter and the total of the additions of propionic ions thereto effects an ultimate concentration of propionic ions therein at least as great as about 0.050 mole/liter.

No references cited. 

1. IN THE CONTINUOUS PROCESS OF CHEMICALLY PLATING WITH NICKEL ARTICLE ESSENTIALLY COMPRISING AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT, NICKEL, ALUMINUM, COPPER, SILVER, GOLD, PALLADIUM AND PLATINUM; WHEREIN AND ARTICLES ARE CONTACTED WITH A BATH COMPRISING AN AQUEOUS SOLUTION OF NICKEL IONS AND HYPOPHOSPHITE IONS AND LACTIC IONS AND PROPIONIC IONS; AND WHEREIN SAID BATH INITIALLY COMPRISES AN ABSOLUTE CONCENTRATION OF HYPOPHOPSHITE IONS IN THE RANGE 0.15 TO 0.30 MOLE/LITRE, SUFFICIENT NICKEL IONS TO PROVIDE A RATIO BETWEEN THE NICKEL IONS AND THE HYPOPHOSPHITE IONS IN THE RANGE 0.25 TO 0.60, AN ABSOLUTE CONCENTRATION OF LACTIC IONS OF ABOUT 0.30 MOLE/LITRE, AND AN ABSOLUTE CONCENTRATION OF PROPIONIC IONS OF ABOUT 0.03 MOLE/LITER, AND SAID BATH HAS AN INITIAL PH IN THE RANGE 4.5 TO 4.8; THE METHOD OF REGENERATING SAID BATH AS THE CONTINUOUS PLATING PROCESS PROCEEDS COMPRISING PROGRESSIVELY ADDING THERETO NICKEL IONS AND HYPOPHOSPHITE IONS AND LACTIC IONS AND PROPIONIC IONS, WHEREBY SAID PROGRESSIVE ADDITIONS OF NICKEL IONS AND HYPOPHOSPHITE IONS ARE SUCH AS TO PREVENT THE DEPLETIONS THEREOF IN SAID BATH AS THE CONTINUOUS PLATING PROCESS PROCEEDS AND SAID PROGRESSIVE ADDITIONS OF LACTIC IONS AND PROPIONIC IONS ARE SUCH AS TO INCREASE PLATING PROCESS THEREOF IN SAID BATH AS THE CONTINUOUS PLATING PROCESS PROCEEDS, WHEREIN SAID ADDITIONS OF LACTIC IONS AND PROPIONIC IONS ARE RELATED TO SAID ADDITION OF NICKEL IONS SO THAT ABOUT 0.03 MOLE OF LACTIC IONS SO OF PROPIONIC IONS ARE ADDED TO SAID BATH TO EACH 0.08 MOLE OF NICKEL IONS ADDED THERETO. 